Temperature, humidity won't sink this U-boat

More than a half-century has passed since the German U-505 submarine was captured during World War II, but the curators at the Museum of Science and Industry in Chicago strive to keep the sub looking in fighting shape. Since the U-boat's capture in 1944, it has survived a near sinking, a treacherous tow from the Atlantic to the Great Lakes, and 50 years of bitter Chicago weather in its post as an outdoor exhibit at the museum.

In 1997, the museum began a restoration project designed to preserve the U-505 and move it indoors to a climate-controlled environment. Presently, the submarine resides on a specially constructed 75 x 42 ft underground exhibit space at the Museum of Science and Industry. To preserve the U-Boat's external and internal structure, the exhibit space was engineered for the most precise temperature and humidity control.

Primera , an engineering and design management firm in Chicago, was selected to design a space and mechanical system that would protect the sub from environmental damage, while providing a comfortable indoor space for museum patrons. Primera wanted to maintain a constant year-round environmental temperature and relative humidity.

“We wanted to maintain a year-round environment of 72 to 75 F with a near-constant relative humidity of 40%. Each additional point of humidity would accelerate the degradation of wood and metal on the sub,” said Ken Panucci, mechanical engineer at Primera.

The problems Primera faced involved developing the system around Chicago's broad spectrum climate, spatial limitations, and the inefficiencies of the existing chilled water system. The previous chilled water system could provide only a 44 F supply temperature. Since Chicago's summers can get hot and humid, the supply temperature was not low enough to provide adequate cooling and dehumidification. Additionally, the traditional method of overcooling the air and then heating it back up would prove very inefficient. Originally, designers considered active dehumidification options typically found in natatorium applications, but the heat energy required to regenerate the desiccant was not cost-effective. The exhibit also featured both sound effects and interactive options, which caused noise control problems. Ultimately, the system would also need to deliver 20,000 cfm of conditioned outdoor air to a limited exhibit space.

“An exhibit decision dropped a section of the floor just adjacent to the mechanical room that forced some redesign to get the SEMCO unit into the available space. The comfort has been ideal with no report of any noise issues,” said Bill Vanderbilt, facilities director for the museum.

Primera selected a Pinnacle Primary Ventilation and Energy Recovery System from SEMCO to solve the problems. The Pinnacle's passive dehumidification wheel uses a desiccant material that is optimized to remove moisture from a saturated airstream without an active regeneration source. The wheel also uses a cooling coil, heating coil, total energy recovery wheel, and a humidifier for wintertime operation.

The Pinnacle system precools and dehumidifies outdoor air during the cooling season and preheats and humidifies the outdoor air during the heating season. The system responds to variations in temperature and humidity by modulating the rotational speed of the passive dehumidification wheel, and adjusting the energy input to the cooling coil. The rotational speed control may be adjusted to control the level of temperature and moisture exchanged by the passive dehumidification wheel. The chilled water coil is sequenced on when the space requires cooling and when the chillers are in operation, from May through October. The heating coil is used only during wintertime operation to boost the supply air temperature. The heat wheels provide approximately three-fourths of the heat required for wintertime operation.

In an effort to maximize efficiency but still maintain fresh air, the system operates with 100% outdoor air during operating hours, if the air can be used for cooling. When outdoor weather is extreme, the system uses just enough outdoor air to maintain proper ventilation. When the museum is closed, the system operates on 50% outside air. The end result is a system that works in harmony with the museum's central chilled water system without any of the energy penalties associated with conditioning 100% outside air in an area with diverse climate conditions. Equally important, the U-505 shows no signs of aging and should continue to educate future generations.

Primera's completed design modeling demonstrated how the SEMCO system would provide annual energy savings of more than $150K over a conventional system that uses the overcooling and reheat function.

Information provided by SEMCO.

AT A GLANCE

The curators at the Museum of Science and Industry in Chicago strive to keep the German U-505 submarine from succumbing to more than 50 years of environmental damage.

Primera was selected to design a mechanical system that would protect the sub from environmental damage. Primera wanted to maintain a constant year-round temperature between 72 and 75 F and relative humidity of 40%. Primera selected a Pinnacle Primary Ventilation and Energy Recovery System from SEMCO to solve the problems.

The Pinnacle system precools and dehumidifies outdoor air during the cooling season and preheats and humidifies the outdoor air during the heating season.